1. Field of the Invention
This invention relates to a semiconductor pressure sensor device including a semiconductor pressure sensor chip mounted on a resin package for detecting a negative pressure.
2. Description of the Related Art
Generally, a semiconductor pressure sensor chip utilizing a piezoresistance effect is adopted as a pressure detecting element to a pressure sensor device for detecting an intake pressure of an automotive engine. This kind of pressure sensor chip includes several diffusion resistors. The diffusion resistors are disposed on a diaphragm made of a material (for instance, single crystal silicon) capable of providing the piezoresistance effect, and are connected into a bridge circuit. A pressure signal is taken out from the bridge circuit in accordance with changes in resistance values of the diffusion resistors which are caused by displacement of the diaphragm.
The pressure sensor chip is conventionally mounted on a resin package. For instance, the sensor chip is disposed on a sensor mount part of the resin package through adhesive by die bonding, and is electrically connected to a conductive part through conductive wires. The conductive part is formed at the resin package side by insert-molding. The pressure sensor chip and the bonding wires are covered with a protective member made of an insulating material to protect them from corrosion, and to secure those insulating performance. In this case, a gel-like insulating material is generally used as the protective member not to inhibit the displacement of the diaphragm.
The covering step by the protective member is carried out under a vacuum atmosphere to prevent voids from being produced in the protective member and within a region covered by the protective member. However, it is very difficult to completely remove air existing in a gap produced between the resin package and the conductive part formed by insert-molding. In addition, the surface of the conductive part is usually plated with gold having low affinity. This results in low adhesiveness between the gel-like protective member and the surface of the conductive part, thereby allowing a state where air is trapped at the interface part.
Because of this, when the semiconductor pressure sensor device detects a negative pressure such as an engine intake pressure, voids produced by air described above within the gel-like protective member grow. The grown voids may move within the gel-like protective member to cause deterioration of the insulating performance and breakage of the wire bonding.
When the semiconductor pressure sensor chip is mounted on a ceramic package by utilizing a wire-bonding technique as disclosed in U.S. Pat. No. 5,357,673, generation of voids can be suppressed as compared to the case adopting the resin package case described above. However, the ceramic package also necessitates bonding pad parts, and therefore, it is difficult to prevent voids from being produced at the interface between the bonding pad parts and the protective member. In addition, since the ceramic package is composed of several members, a number of parts is increased.